A building such as an office building, a residential building, or a hotel includes a switching house in which a switchboard for knife switches is mounted. Common household electric current of hundreds of amperes is distributed to a plurality of output circuits after passing through the switchboard. A plurality of lights are connected in parallel in each output circuit. On/off of each light is controlled by a switch that is connected in series to the light, as shown in FIG. 1.
However, on/off of each light can only be controlled via the associated switch, which is relatively inconvenient. Further, the wiring procedure is troublesome and many switches are required for the control system, leading to a high equipment cost. Further, installation of the control system is complicated and thus results in a high cost. Further, maintenance of the control system is not easy.